A magnetic matrix display of the present invention is particularly although not exclusively useful in flat panel display applications such as television receivers and visual display units for computers, especially although not exclusively portable computers, personal organizers, communications equipment, and the like.
Conventional flat panel displays, such as liquid crystal display panels and field emission displays, are complicated to manufacture because they each involve a relatively high level of semiconductor fabrication, delicate materials, and high tolerances.
GB Patent Application 2304981 discloses a magnetic matrix display having a cathode for emitting electrons, a permanent magnet with a two dimensional array of channels extending between opposite poles of the magnet, the direction of magnetisation being from the surface facing the cathode to the opposing surface. The magnet generates, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam. The display also has a screen for receiving an electron beam from each channel. The screen has a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of pixels each corresponding to a different channel.
The magnetic matrix display uses a thick glass for the screen and backplate in order to ensure that a self supporting structure can be obtained when the glass envelope is evacuated. The thickness of glass required to provide this self supporting structure effectively limits this type of design to screen diagonals up to about 24 inches (610 mm).
To allow screen sizes with a larger than 24 inch (610 mm) diagonal, or to allow the thickness of the glass and hence the weight of the display to be reduced, thinner glass must be used. This requires the use of front spacers and back supports to withstand the atmospheric pressure on the outside of the glass envelope due to the vacuum within the glass envelope. Such spacers and supports can be designed, but the permittivity of an insulating support modifies the position of the remote cathode and changes the electron density in the vicinity of the support. This effects grid cutoff and the emission of electrons. The permittivity of an insulating spacer modifies the electrostatic field patterns in the vicinity of the spacer or of the support and hence will change the shape and/or direction of the electron beam.
Thus a visible pattern will appear on the screen at the locations where the spacers or the supports are located. If one component (spacer or support) is used between every pixel of the screen, then such visible patterning will not cause a problem, since it will be consistent across the whole area of the screen. In a practical design, such spacers and supports are positioned at intervals of about 10 mm and so the patterning can be discerned in the screen image generated by the display.